Field of the Invention
The present invention relates to a toner that is used to form a toner image through the development of an electrostatic latent image formed by a method such as electrophotography, electrostatic recording, and toner jet system recording methods.
Description of the Related Art
Higher productivities and the ability to output high-definition full-color images have been required of copiers and printers in a broad field from the office to the home in recent years. Within this context, users are making a wide range of demands, i.e., increasing copying machine and printer speed is important and at the same time there is demand for the image quality required to print photographs and for the ability to print images that have small edge margins.
Increasing the speed of a copying machine or printer first of all means increasing the speed of the developing system. The developing system is an image-forming process that uses toner to bring about a visualization of the electrostatic latent image. Its operation is accompanied by both toner-to-toner contact and toner-to-component member contact, and the toner is repetitively subjected to loading each time this contact occurs. The toner ends up being degraded by this loading and the flowability and tribochargeability required for performance as a developer then undergo a gradual decline. In addition, it has been found that toner in this condition presents a reduced amount of charge and a nonuniform charge distribution, resulting in the occurrence of image defects.
To respond to these problems, for example, Japanese Patent Application Laid-open No. 2007-171272 proposes a toner having a core-shell structure in which a shell layer coats a core particle that contains a binder resin, colorant, and release agent, and having a certain prescribed range specified for its average fracture strength. With this method, an art is disclosed that brings about an improvement in the ability of the toner to resist the degradation due to the loading that the toner receives. In the case of core-shell structures, there is a clear strengthening with respect to the loading to which the toner is repetitively subjected. However, with methods in which the toner particle is produced in an aqueous medium, such as the suspension polymerization method used in Japanese Patent Application Laid-open No. 2007-171272, the wax tends to segregate to the neighborhood of the center of the toner. As a consequence, outmigration of the wax from the toner during fixing is impeded and wraparound on the fixing member tends to occur easily in the case of an image having small edge margins.
Japanese Patent Application Laid-open No. 2010-122667 therefore proposes, for solution suspension methods where toner production is carried out using an aqueous medium, a method of dispersing the wax in the toner using a wax dispersing agent. The wax is definitely dispersed in the toner particle and wax is also present in the neighborhood of the toner surface. Compatibility between the binder resin and wax during fixing is facilitated as a result, and due to this an effect on the low-temperature fixability appears. However, when the binder resin and wax are compatible, this is not effective with regard to the separation behavior of the paper due to a loss of the functional effect as a wax.